Converting loess into zeolite for heavy metal polluted soil remediation based on "soil for soil-remediation" strategy

Assessing the exposure of lead, cadmium, and arsenic on growth parameters and antioxidant defense system in wheat

Heavy metals (HMs) pollution of soil adversely impacts agricultural productivity and poses risks to public health, necessitating regular and timely monitoring of HMs accumulation in soils. Wheat (Triticum aestivum L.), as a globally cultivated staple crop, is particularly vulnerable to HM-induced stress, which can significantly reduce its yield and quality. The purpose of the experiment was to study the effect of lead (Pb), cadmium (Cd), and arsenic (As) on the growth, photosynthetic pigments content, enzymatic and low molecular weight antioxidants, and the uptake of metals in the wheat seedlings. We carried out a pot experiment in which HMs were introduced into the soil Pb (1300 mg kg-1), Cd (20 mg kg-1), As (100 mg kg-1) separately and all together in one combination and an uncontaminated control. The doses of HMs corresponded to the registered high pollution level in impact zone (10 approximate permissible concentrations). The results showed that HMs contamination of the soil affected the growth, photosynthetic pigments and antioxidant enzymes activities in wheat. The polyelement contamination significantly reduced root growth. The polyelement contamination led to an intensification of lipid peroxidation processes, which was reflected in an increase in malondialdehyde content in leaves and roots by 39% and 127% compared with the control. The cumulative exposure affected antioxidants in wheat, leading to deregulation of defense mechanisms, characterized by an increase in reduced glutathione content in leaves and roots by 23% and 69%, an increase in proline and ascorbic acid content in leaves by 174% and 20%, and a decrease in roots by 80% and 43%, respectively. These results highlight that HMs contamination not only inhibited growth but also affected antioxidant defense system. Therefore, developing effective strategies to mitigate HMs-induced stress and enhance wheat production is crucial for sustainable agriculture in contaminated environments.

Zeolite with Remarkable Pb2+ and Cd2+ Removal Capability Cost-Effectively Synthesized from Postprocessed Natural Stellerite

MER zeolite, a low-silica zeolite with an 8-membered ring aluminosilicate framework, has been recognized as a promising material in sorption, separation, and ion-exchange applications. Herein, we developed a cost-effective and rapid method to convert parent zeolite H-STI, which was derived from natural stellerite, into MER zeolite through interzeolite conversion with a crystallization time of 8 h. This MER zeolite exhibits high efficiency in removing Pb2+ and Cd2+ from simulated heavy metal wastewater over a pH range of 3-8. It also shows excellent selectivity in the presence of competitive cations, including Na+, K+, Ca2+, Mg2+, Zn2+, Cu2+, and Co2+. At 25 °C, with a MER-S dosage of 1/3000 g·mL-1 for Pb2+ and 1/500 g·mL-1 for Cd2+, the removal efficiencies were 99.7 and 99.9%, respectively. The distribution coefficients were 1097 L·g-1 for Pb2+ and 550 L·g-1 for Cd2+, and the sorption capacities reached 513 mg·g-1 for Pb2+ and 171 mg·g-1 for Cd2+, indicating that the product MER zeolite is one of the highest sorbents for Pb2+ and Cd2+ reported for zeolitic materials. The sorption for Pb2+ and Cd2+ both follows the chemisorption-dominated mechanism, driven by the ion-exchange process between the K+ in the channels MER-S and the Pb2+ or Cd2+ in solution. This work highlights the potential of rapidly synthesized MER zeolite for the effective removal of heavy metal cations, emphasizing its performance and practical applicability.

Synthesis and Characterization of NaX Zeolite from Coal Gangue and Its Efficacy in Cd and Pb Remediation in Water and Soil

Alkaline fusion is a pivotal process influencing the cost of synthesizing zeolite from coal gangue. This study examined the effects of alkaline fusion temperature (X 1), treatment duration (X 2) and the NaOH/coal gangue weight ratio (X 3) on the composition and properties of the products, as well as their adsorption capacities for Cd2+ (q e,Cd) and Pb2+ (q e,Pb). Response surface methodology (RSM) was employed to analyze the interactions among these factors, and the adsorption mechanisms for Cd2+ and Pb2+ were investigated using X-ray diffraction, scanning electron microscopy-EDS, Fourier transform infrared, X-ray photoelectron spectroscopy, and N2 adsorption-desorption techniques. The results reveal that (1) under optimized conditions-X 1 of approximately 800 °C, X 2 of around 2.8 h and X 3 of 1.2-the maximum q e,Cd and q e,Pb for the synthesized NaX zeolite can reach 181.3 and 419.9 mg/g, respectively. (2) The RSM models indicate that increasing the X 3 value can lower the required X 1. For q e,Cd and q e,Pb of 150 and 350 mg/g, respectively, with X 2 fixed at 2 h, increasing X 3 from 0.976 to 1.134 and from 0.900 to 1.289 enables a reduction in X 1 from 800 to 600 °C. (3) NaX zeolite primarily adsorbs Cd2+ and Pb2+ through ion exchange, allowing these ions to enter the zeolite's cage structure. Pb2+ can also precipitate as hydrocerussite (Pb3(CO3)2(OH)2) within the zeolite channels, while Cd2+ has a more significant impact on the [SiO4] and [AlO4] tetrahedra. (4) The synthesized NaX zeolite effectively reduces the exchangeable Cd content in contaminated soil from 3.51 to below 1.5 mg/kg. The remediation performance of the NaX zeolite for Cd and Pb in water and soil can be further enhanced by optimizing its Si/Al ratio and pore structure.

Composites Based on Natural Zeolites and Green Materials for the Immobilization of Toxic Elements in Contaminated Soils: A Review

Soil contamination by toxic elements is a global problem, and the remediation of contaminated soils requires complex and time-consuming technology. Conventional methods of soil remediation are often inapplicable, so an intensive search is underway for innovative and environmentally friendly ways to clean up ecosystems. The use of amendments that stabilize the toxic elements in soil by reducing their mobility and bioavailability is one of the simplest and most cost-effective ways to remediate soil. This paper provides a summary of studies related to the use of composites based on natural zeolites and green materials for the immobilization of toxic elements in contaminated soils and highlights positive examples of returning land to agricultural use. The published literature on natural zeolites and their composites has shown that combinations of zeolite with biochar, chitosan and other clay minerals have beneficial synergistic effects on toxic element immobilization and soil quality. The effects of zeolite properties, different combinations, application rates, or incubation periods on toxic elements immobilization were tested in laboratory scale or field experiments, whereas the mobility of toxic elements in soil was evaluated by chemical extractions of toxic elements transferred to the plants. This review highlights the excellent potential of natural zeolites to be used as single or combined sustainable green materials to solve environmental pollution problems related to the presence of toxic elements.

Application of acid-activated attapulgite clay on effective immobilization of Cd in paddy soils

This study investigated the effects of different amounts of acid-activated attapulgite clay on soil environmental risks and ecotoxicity after incubation as a soil amendment. The experimental soil was alkaline clay soil with a pH of 7.54. The optimal addition and incubation times for the remediation of Cd-contaminated soil were determined. The results showed that the optimal period for Cd stabilization was 24 days, and the optimal addition amount was 8% (w/w). The addition of 8% attapulgite clay significantly reduced the bioavailable Cd concentration in soil. Water-Cd, DTPA-Cd, TCLP-Cd, and HCl-Cd reduced the bioavailable Cd concentration in the soil by 26.43%, 42.75%, 35.22%, and 25.89%, respectively. Meanwhile, the addition of 8% attapulgite clay converted the chemical speciation of exchangeable-Cd into residual-Cd, and the stabilizing component increased by 48% after 48 days. The ecological and environmental risk indices decreased significantly, reaching 10.89% and 4.22%, respectively. The pot experiment showed that attapulgite clay promoted corn growth while decreasing concentrations of Cd in aboveground parts and roots by 9.01-31.82% and 9.52-40.48%, respectively, and limited Cd transfer from roots to stems, minimizing its presence in edible portions as much as possible. The accumulation of heavy metals in the growth of corn plants was significantly and positively correlated with the bioavailability of Cd extracted from different extractants and exchangeable speciation, and significantly and negatively correlated with soil residual speciation. Attapulgite is a promising soil amendment that can effectively reduce ecological and environmental risks, reduce the ecological toxicity of Cd, and improve soil quality.

Harnessing plant extracts for eco-friendly synthesis of iron nanoparticle (Fe-NPs): Characterization and their potential applications for ameliorating environmental pollutants

Iron-nanoparticles (Fe-NPs) are increasingly been utilized in environmental applications due to their efficacy and strong catalytic activities. The novelty of nanoparticle science had attracted many researchers and especially for their green synthesis, which can effectively reuse biological resources during the polymerization reactions. Thus, the synthesis of Fe-NPs utilizing plant extracts could be considered as the eco-friendly, simple, rapid, energy-efficient, sustainable, and cost-effective. The green synthesis route can be recognized as a practical, valuable, and economically effective alternative for large-scale production. During the production process, some biomolecules present in the extracts undergo metal salts reduction, which can serve as both a capping and reducing mechanism, enhancing the reactivity and stability of green-synthesized Fe-NPs. The diversity of species provided a wide range of potential sources for green synthesis of Fe-NPs. With improved understanding of the specific biomolecules involved in the bioreduction and stabilization processes, it will become easier to identify and utilize new, potential plant materials for Fe-NPs synthesis. Newly synthesized Fe-NPs require different characterization techniques such as transmission electron microscope, ultraviolet-visible spectrophotometry, and X-ray absorption fine structure, etc, for the determination of size, composition, and structure. This review described and assessed the recent advancements in understanding green-synthesized Fe-NPs derived from plant-based material. Detailed information on various plant materials suitable of yielding valuable biomolecules with potential diverse applications in environmental safety. Additionally, this review examined the characterization techniques employed to analyze Fe-NPs, their stability, accumulation, mobility, and fate in the environment. Holistically, the review assessed the applications of Fe-NPs in remediating wastewaters, organic residues, and inorganic contaminants. The toxicity of Fe-NPs was also addressed; emphasizing the need to refine the synthesis of green Fe-NPs to ensure safety and environmental friendliness. Moving forward, the future challenges and opportunities associated with the green synthesis of Fe-NPs would motivate novel research about nanoparticles in new directions.

Effects of environmental metal and metalloid pollutants on plants and human health: exploring nano-remediation approach

Metal and metalloid pollutants severely threatens environmental ecosystems and human health, necessitating effective remediation strategies. Nanoparticle (NPs)-based approaches have gained significant attention as promising solutions for efficient removing heavy metals from various environmental matrices. The present review is focused on green synthesized NPs-mediated remediation such as the implementation of iron, carbon-based nanomaterials, metal oxides, and bio-based NPs. The review also explores the mechanisms of NPs interactions with heavy metals, including adsorption, precipitation, and redox reactions. Critical factors influencing the remediation efficiency, such as NPs size, surface charge, and composition, are systematically examined. Furthermore, the environmental fate, transport, and potential risks associated with the application of NPs are critically evaluated. The review also highlights various sources of metal and metalloid pollutants and their impact on human health and translocation in plant tissues. Prospects and challenges in translating NPs-based remediation from laboratory research to real-world applications are proposed. The current work will be helpful to direct future research endeavors and promote the sustainable implementation of metal and metalloid elimination.

Sources, effects and present perspectives of heavy metals contamination: Soil, plants and human food chain

Heavy metal (HM) poisoning of agricultural soils poses a serious risk to plant life, human health, and global food supply. When HM levels in agricultural soils get to dangerous levels, it harms crop health and yield. Chromium (Cr), arsenic (As), nickel (Ni), cadmium (Cd), lead (Pb), mercury (Hg), zinc (Zn), and copper (Cu) are the main heavy metals. The environment contains these metals in varying degrees, such as in soil, food, water, and even the air. These substances damage plants and alter soil characteristics, which lowers crop yield. Crop types, growing circumstances, elemental toxicity, developmental stage, soil physical and chemical properties, and the presence and bioavailability of heavy metals (HMs) in the soil solution are some of the factors affecting the amount of HM toxicity in crops. By interfering with the normal structure and function of cellular components, HMs can impede various metabolic and developmental processes. Humans are exposed to numerous serious diseases by consuming these affected plant products. Exposure to certain metals can harm the kidneys, brain, intestines, lungs, liver, and other organs of the human body. This review assesses (1) contamination of heavy metals in soils through different sources, like anthropogenic and natural; (2) the effect on microorganisms and the chemical and physical properties of soil; (3) the effect on plants as well as crop production; and (4) entering the food chain and associated hazards to human health. Lastly, we identified certain research gaps and suggested further study. If people want to feel safe in their surroundings, there needs to be stringent regulation of the release of heavy metals into the environment.

Impurities in Polymer-Lined Autoclaves Affect Zeolite Synthesis and Si Incorporation Behavior

Polymer-lined autoclaves are commonly believed to be highly durable and inert in hydrothermal reactions. Herein, we use the hydrothermal synthesis of AlPO-18 zeolite as a case study to demonstrate that the choice of autoclave materials (polytetrafluoroethylene or para-polyphenylene) does significantly affect the product of zeolite synthesis. A small amount of glass fiber in the PPL-lined autoclave unexpectedly functions as a source of silicon and yields SAPO-34 instead of AlPO-18 as the product. The outcomes of 19 successive experiments conducted with a single PPL-lined autoclave exhibit significant variations, further highlighting that the impurities arising from the autoclaves should be considered during the hydrothermal synthesis procedure. In contrast to SAPO-34 synthesized by the conventional method, which displays only Si(4Al) at a low Si/Al ratio, SAPO-34 synthesized in the PPL-lined autoclave exhibits multiple silicon coordination environments. This outcome provides new physical insights into the silicon incorporation mechanism and proposes a viable strategy for regulating the silicon coordination environment at low Si/Al ratios.

Study on the solidification performance and mechanism of heavy metals by sludge/biomass ash ceramsites, biochar and biomass ash

Industrial by-products are stored in large quantities in the open, leading to wasted resources and environmental pollution, and the natural environment is similarly faced with phosphate depletion and serious water and soil pollution. This study uses these by-products to produce a new sludge/biomass ash ceramsite that will be used to adsorb nitrogen and phosphorus from wastewater, and solidify heavy metals in the soil while releasing Olsen P. The sludge/biomass ash ceramsites are made using sewage sludge and biomass ash in a certain ratio calcined at high temperatures and modified for the adsorption of nitrogen and phosphorus from wastewater. Sludge/biomass ash ceramsites before and after phosphorus adsorption, biochar and biomass ash were compared to analyze their heavy metal adsorption capacity and potential as phosphate fertilizer. After phosphorus adsorption, the sludge/biomass ash ceramsites released effective phosphorus steadily and rapidly in the soil, with a greater initial release than biochar and biomass ash, and the ceramsites were in a granular form that could be easily recycled. Biochar and biomass residue, due to their surface functional groups, are better at solidifying heavy metals than sludge/biomass ash ceramsites. Biochar, biomass ash and sludge/biomass ash ceramsites significantly reduced the concentrations of Cd, Cu, Pb and Zn in the soil. Correlation analysis demonstrated that there was a synergistic relationship between the increase in soil Olsen P content and the change in pH, with the increase in soil Olsen P content and the increase in pH contributing to heavy metal solidification.

Migration of spent grain-modified colloidal ferrihydrite: Implications for the in situ stabilization of arsenic, lead, and cadmium in co-contaminated soil

The increase of metal mining, processing, and smelting activities has precipitated a substantial escalation in the contamination of soil by heavy metals. Ferrihydrite (FH) has been commonly used as an amendment for the immobilization of heavy metals in contaminated soil. However, FH suffers from drawbacks such as agglomeration and nonmigratory characteristics, which limit its practical application in soil remediation. Herein, a novel spent grain-modified ferrihydrite (FH-SG) colloidal system was developed, and the FH-SG transport mechanisms in the soil medium were fully studied, focusing in particular on the simultaneous in situ stabilization of arsenic (As), lead (Pb), and cadmium (Cd) in co-contaminated soil. The results showed that the stabilization rates of the FH-SG material reached 94.66%, 96.12%, and 95.52% for water-soluble As, Pb, and Cd, respectively, and 72.22%, 49.39%, and 25.30% for bioavailable As, Pb, and Cd, respectively. The FH-SG material demonstrates notable migration properties in porous media. Theoretical calculation results of a single collector show that the migration deposition of FH-SG material in media is primarily governed by its inherent diffusion characteristics with minimal influence by gravitational forces and media interception. It is noteworthy that the maximum migration distance in quartz sand and soil media with different particle sizes can reach 2.07-2.92 m and 0.78-1.08 m, respectively. Altogether, our findings clearly demonstrate that FH-SG exhibits better stabilization and migration than those of FH alone and most proposed FH colloidal systems. The FH-SG colloidal system holds significant promise for the remediation of various kinds of complex polluted soil.

Synchronous stabilization of Pb, Zn, Cd, and As in lead smelting slag by industrial solid waste

In order to prevent heavy metal (HM) pollution from lead smelting slag (LSS) to the surrounding environment, this work investigated the feasibility, influencing factors, and mechanisms of using industrial solid waste such as fly ash (FA), oil sludge pyrolysis residue (PR), and steel slag (SS) as remediation amendments. The results demonstrated that the stabilization process was influenced by the material dosage, water content, and LSS particle size. Compared to single materials, the combination amendment PR2FA1 (with a mass ratio of PR to FA as 2:1) exhibited the best stabilization effect, simultaneously reducing the leaching concentrations of As, Zn, Cd, and Pb in LSS to 0.032, 0.034, 0.002, and 0.014 mg/L, respectively. The pH value of the leachate remained between 8 and 9, which met the requirements of surface water quality class IV (GB3838-2002). Through morphological analysis, microscopic characterization, and simulated solution adsorption experiments, it was determined that the stabilization process of HMs was controlled by various mechanisms, including electrostatic attraction, physical adsorption, ion exchange, and chemical precipitation. PR2FA1 had more active components, and its fine-porous structure provided more active sites, resulting in good stabilization performance for As, Zn, Cd, and Pb. Furthermore, cost analysis showed that PR2FA1, as an environmentally friendly material, could generate profits of 157.2 ¥/ton. In conclusion, the prepared PR2FA1 not only addressed the HMs pollution from lead smelting slag to the surrounding environment but also achieved the safe and resourceful disposal of hazardous waste-oil sludge. Its excellent performance in stabilizing HMs and cost-effectiveness suggested promising commercial applications.

Soil amendments for vanadium remediation: a review of remediation of vanadium in soil through chemical stabilization and bioremediation

Immobilization of vanadium (V) in soils is one option to prevent groundwater contamination and plant uptake. Phytoremediation, microbial remediation, and chemical stabilization using soil amendments are among the leading environmentally friendly and economically feasible techniques in V remediation. Soil amendments were used to reduce V mobility by immobilizing it in the soil matrix through chemical stabilization, while bioremediation methods such as phytoremediation and microbial remediation were used to remove V from contaminated soils. Vanadium exists in several species and among them V5+ species are the most prevalent, toxic, and soluble form and present as a negatively charged ion (H2VO4- and HVO42-) in oxic soils above pH 4. Amendments used for chemical stabilization can change the physicochemical properties enhancing immobility of V in soil. The pH of the soil environment, point of zero charge of the colloid surface, and redox conditions are some of the most important factors that determine the efficiency of the amendment. Commonly used amendments for chemical stabilization include biochar, zeolites, organic acids, various clay minerals and oxides of elements such as iron, titanium, manganese, and aluminum. For bioremediation, chelating agents and microbial communities are used to mobilize V to enhance phyto-or microbial-extraction procedures. The objectives of this review were to discuss remediation methods of V while considering V speciation and toxicity in soil, and soil amendment application for V removal from soil. The information compiled in this review can guide further research on soil amendments for optimal V remediation in largely contaminated industrial sites.

Zoning of some physicochemical parameters in the sediments of Meighan wetland in Iran: response to urbanization, industrial, and agricultural activities

Meighan wetland is located at 8 km far away from Arak city with a population of about 600,000 citizens in the center of Iran. Several agricultural activities and industries such as metal, chemical, and mineral, as well as industrial towns, exist around the desired wetland. This research was conducted to measure the sources of chemical contaminants entering the wetland through natural and artificial waterways, to explore the trend of changes in the contaminants, and to prepare the wetland contamination zone map followed by source detection of these contaminants. Sediment samples were taken during 2019-2020 from a depth of 0-30 cm from 87 points in the input waterways. The results indicated that the mean total concentrations of cadmium, nickel, lead, zinc, copper, and aluminum in sediments were estimated as 6.7, 93.4, 14.1, 276.4, 34.3, and 22,742.7 ppm, respectively. The concentrations of nitrate and phosphate in the sediments were given as 18.6 and 1.8 ppm, respectively. The mean comparison indicated that the most significant level of nickel and lead belonged to the input waterways of industrial and urban regions; the maximum cadmium content was seen in the input waterways from the agricultural lands; and the highest level of zinc and aluminum was recorded in the waterways of agricultural-industrial urban regions. There was a significant relationship between the results of classic statistics and zoning found in GIS. Overall, chemical pollutants with the origin of input wastewater from the treatment plant of wastewater and the input waterways from the industrial and urban regions have had the largest share of contamination for Meighan wetland.

A preliminary study to explain how Streptomyces pactum (Act12) works on phytoextraction: soil heavy metal extraction, seed germination, and plant growth

Streptomyces pactum (Act12) can both promote plant growth and strengthen heavy metal mobilization. Nevertheless, the mechanisms of how Act12 works during the phytoextraction process are still unknown. The present work investigated whether the metabolites produced by Act12 could influence the seed germination and the growth of potherb mustard and explored its mobilizing effect on soil cadmium (Cd) and zinc (Zn). The results showed that the germination potential and rate of potherb mustard seed treated with Act12 fermentation broth were 1.0- and 0.32-folds higher than those of control, probably due to the interruption of seed dormant stage. We also found that Act12 inoculation not only promoted the dry biomass (6.82%) of potherb mustard, but also increased the leaf chlorophyll (11.8%) and soluble protein (0.35%) production. The boosted seed germination rate under Act12 treatment (up to 63.3%) indicated that Act12 enhanced the resistance of potherb mustard seeds to Cd and Zn and alleviated their physiological toxicity. The generated metabolites during the Act12 fermentation posed positive impact on the availability of soil Cd and Zn. These findings bring new insight into the Act12-assisted phytoextraction of Cd and Zn from contaminated soils.

Mobility of arsenic and vanadium in waterlogged calcareous soils due to addition of zeolite and manganese oxide amendments

Addition of manganese(IV) oxides (MnO₂ ) and zeolite can affect the mobility of As and V in soils due to geochemical changes that have not been studied well in calcareous, flooded soils. This study evaluated the mobility of As and V in flooded soils surface-amended with MnO₂ or zeolite. A simulated summer flooding study was conducted for 8 weeks using intact soil columns from four calcareous soils. Redox potential was measured in soils, whereas pH, major cations, and As and V concentrations were measured biweekly in pore water and floodwater. Aqueous As and V species were modeled at 0, 4, and 8 weeks after flooding (WAF) using Visual MINTEQ modeling software with input parameters of redox potential, temperature, pH, total alkalinity, and concentrations of major cations and anions. Aqueous As concentrations were below the critical thresholds (<100 μg L^-1 ), whereas aqueous V concentrations exceeded the threshold for sensitive aquatic species (2-80 μg L^-1 ). MnO₂ -amended soils were reduced to sub-oxic levels, whereas zeolite-amended and unamended soils were reduced to anoxic levels by 8 WAF. MnO₂ decreased As and V mobilities, whereas zeolite had no effect on As but increased V mobility, compared to unamended soils. Arsenic mobility increased under anoxic conditions, and V mobility increased under oxic and alkaline pH conditions. Conversion of As(V) to As(III) and V(V) to V(IV) was regulated by MnO₂ in flooded soils. MnO₂ can be used as an amendment in immobilizing As and V, whereas the use of zeolite in flooded calcareous soils should be done cautiously.

Decreased in vitro bioaccessibility of Cd and Pb in an acidic Ultisol through incorporation of crop straw-derived biochar

Studies analyzing the in vitro bioaccessibility (BAc) of heavy metals in biochar-amended soils are currently lacking. The present study aimed to assess the metal BAc in Cd- and Pb-spiked acidic Ultisol samples treated individually with 2% (w/w) maize, rice, wheat, soybean, and pea straw-derived biochar. The results indicate that the Cd-BAc simulated in gastric phase (GP) decreased from 78.4% to 66.5-72.3% and the Pb-BAC decreased from 74.3% to 67.2-69.2%; however, the Cd-BAc in the intestinal phase (IP) decreased from 35.6% to 27.9-33.5% and the Pb-BAc decreased from 34.7% to 29.7-32.9% after 120 d of incubation with biochar application compared to the un-amended Ultisol. The Cd- and Pb-BAc in both GP and IP were significantly negatively correlated with soil pH, CEC, and organic carbon (P < 0.05), which increased after biochar application. The soybean straw-derived biochar amendment has the greatest potential to decrease the BAc of Cd and Pb in the GP and IP, owing to the highest level of CEC, SOC, TC and TN among all soil samples. Moreover, the BAc was positively correlated with the exchangeable, and exchangeable + carbonate-bound Cd and Pb fractions (P < 0.05), indicating these fractions had a dominant influence on the BAc of cationic heavy metals. Therefore, crop straw-derived biochar amendment can decrease the BAc of Cd and Pb in acidic Ultisol, and thus mitigate the health risks posed by these metals from incidental ingestion.

Self-regulated immobilization behavior of multiple heavy metals via zeolitization towards a novel hydrothermal technology for soil remediation

More efficient soil remediation technologies are highly anticipated to treat large quantities of heavy metal-polluted urban sites nowadays. Herein, a novel hydrothermal technology of converting heavy metal-polluted soils into zeolites for in-situ immobilizing heavy metals was proposed. The zeolites (analcime and cancrinite) could be synthesized hydrothermally with certain Na/Si and Al/Si ratios. The formed zeolites could manage to change their species and structure during zeolitization to accommodate different heavy metals in soil according to their size and charge. Since smaller-size Cu²⁺ was introduced, analcime and some cancrinite possessing small cages could be formed adaptively to immobilize the Cu²⁺ by replacing Na⁺ and forming Cu²⁺-OH and Cu²⁺-O. Whereas, cancrinite with large channels managed to form to immobilize the larger-size Cd²⁺ by forming Cd²⁺-O. Interplanar spacing variation of zeolites also corresponded to their structural change for accommodating different heavy metals. Leaching results showed the amounts of Cu and Cd leached from the synthesized zeolites were reduced to 0.005% and 0.05% respectively, reflecting a more stable immobilization of smaller heavy metals by small cages, in agreement with the results of distribution coefficient (K_d). Negligible effect of pH environment on the leaching rates further confirmed the stable structural immobilization of heavy metals by zeolites.

Stabilization of lead and cadmium in soil by sulfur-iron functionalized biochar: Performance, mechanisms and microbial community evolution

Sulfur-iron functionalized biochar (BC-Fe-S) was designed by simultaneously supporting Fe₂O₃ nanoparticles and grafting sulfur-containing functional groups onto biochar to stabilize Pb and Cd in soil. The BC-Fe-S exhibited excellent stabilization performance for Pb and Cd with fast kinetic equilibrium within 5 days associating with pseudo-second-order model. The bioavailable-Pb and -Cd contents decreased by 59.22% and 70.28% with 3% BC-Fe-S treatment after 20 days of remediation. Speciation transformation analysis revealed that the increase of stabilization time and BC-Fe-S dosage with appropriate soil moisture and pH promoted toxicities decrease of Pb and Cd with transformation of labile fractions to more steady fractions. The labile fractions of Pb and Cd decreased by 12.22% and 16.21% with 3% BC-Fe-S treatment, and transformed to the residual speciation. Meanwhile, wetting-drying and freezing-thawing aging did not markedly alter the bioavailability of Pb and Cd, proving that the BC-Fe-S holds promise for stabilization of Pb and Cd in varying environmental conditions. 16S rRNA sequencing analysis demonstrated that the BC-Fe-S significantly improved diversity and composition of microbial community, especially increasing the relative abundance of heavy metal-resistant bacteria. Overall, these results suggested BC-Fe-S as a high-performance and environmental-friendly amendment with stability to remediate heavy metals polluted soil.

Transferring waste red mud into ferric oxide decorated ANA-type zeolite for multiple heavy metals polluted soil remediation

Herein, a novel "waste reclamation for soil remediation" strategy has been developed for both alkaline waste red mud (RM) recycling and heavy metal (HM) polluted soil remediation. Through a direct one-pot hydrothermal reaction process, the Al, Si, alkali, and Fe₂O₃ components in waste RM have been transferred into ferric oxide decorated ANA-type zeolite (Fe₂O₃-ANA). As tested by the HMs polluted soil remediation and oilseed rape planting experiment, when 25 g/kg Fe₂O₃-ANA is added into the Pb²⁺, Cu²⁺, Cr³⁺ and anionic AsO₂^- polluted soil (HM concentration: 100-200 mg/kg), it can effectively suppress the HMs mobility in soil and reduce the bio-accumulation concentrations of HMs in the harvested oilseed rape (reduce ratio: 37.9-69.5%). The detailed mechanism study using energy dispersive X-ray energy spectroscopy, in-depth X-ray photoelectron spectroscopy and density function theory calculation concludes that the Cu²⁺, Pb²⁺ and Cr³⁺ in soil have been adsorbed and trapped in the framework structure of ANA in Fe₂O₃-ANA mainly via the cation exchange process. While the anionic AsO₂^- species are mainly caught by the Fe₂O₃ component in Fe₂O₃-ANA via surface adsorption. Overall, this work firstly transforms waste RM into Fe₂O₃-ANA for soil remediation, which is valuable to waste resource recycling and environmental conservation.

Current trends and future prospective in nanoremediation of heavy metals contaminated soils: A way forward towards sustainable agriculture

Heavy metals (HMs) contamination in agricultural soils is a major concern for global food safety and human health. Although, various in-situ and ex-situ remediation methods have been used for the treatment of HMs contaminated soils, however, they also have many drawbacks viz., capital investment, toxicity, and environmental health hazards. Consequently, there is an urgent need to develop a novel method to ameliorate the toxicity of HMs in agricultural soils. In recent years, nanoparticles (NPs) have gained significant attention due to their potential applications in the environment and agriculture fields. Nanoremediation employs NPs that effectively reduce the contents of toxic HMs in the soil-plant system. Several studies have reported that the application of NPs in HMs-polluted soils, which reduced plant-available HMs concentration soils. However, the long-term efficiency of NPs immobilization is still unclear. Here, we provide details about the toxicity of HMs to environmental systems and potential applications NPs to alleviate the accumulation of HMs in agricultural soils. Finally, we present the mechanistic route of HMs-toxicity alleviation in plants by NPs application as well as their long-term efficiency and future prospects.

Kinetics, thermodynamics, equilibrium, surface modelling, and atomic absorption analysis of selective Cu(ii) removal from aqueous solutions and rivers water using silica-2-(pyridin-2-ylmethoxy)ethan-1-ol hybrid material

The removal of heavy metals is attracting considerable attention due to their undesirable effects on the environment. In this investigation, a new adsorbent based on silica functionalized with pyridin-2-ylmethanol (SiPy) was successfully synthesized to yield to a hybrid material. FTIR, SEM, TGA, and specific surface area analysis were used to characterize the structure and morphology of the SiPy hybrid material. Various heavy metal ions such as Cu(ii), Zn(ii), Cd(ii), and Pb(ii) were selected to examine the adsorption efficiency of the newly prepared adsorbent, optimized at varying solution pH, contact time, concentration, and temperature. The adsorbent SiPy displayed good adsorption capacity of 90.25, 75.38, 55.23, and 35.12 mg g⁻¹ for Cu(ii), Zn(ii), Cd(ii), and Pb(ii), respectively, at 25 min and pH = 6. The adsorption behaviors of metal ions onto the SiPy adsorbent fitted well with the pseudo-second-order kinetic mode and the isotherm was better described by the Langmuir isotherm. The thermodynamic studies disclose spontaneous and endothermic adsorption process. Furthermore, the SiPy adsorbent retained good selectivity and regeneration properties after five adsorption–desorption cycles of Cu(ii). A computational investigation of the adsorption mechanism indicates that the N-pyridine, O-hydroxyl, and ether O-atoms play a predominant role during the capture of Cu(ii), Zn(ii), Cd(ii), and Pb(ii). This study proposes the SiPy adsorbent as an attractive material for the selective removal of Cu(ii) from real river water and real industrial wastewater.

The removal of heavy metals is attracting considerable attention due to their undesirable effects on the environment.